Seven-membered ring (septanose) oligosaccharides are unknown in nature, since natural sugars have a thermodynamic preference of five- and six-membered rings, such as furanose and pyranose. Grindley et al. J. Chem. Soc., Chem. Commun. (1978) 1073. Though not naturally occurring, seven-membered ring sugar synthesis has been demonstrated via synthetic methods utilizing extensive protective group manipulations of secondary alcohols of hexose sugars or by rearrangements of appropriately protected furanoside derivatives. Stevens et al. J. Chem. Soc., Chem. Commun. (1969) 1140; Ng et al. Carbohydr. Res. (1996) 284:241; Tran et al. Aust. J. Chem. (2002) 55:171; Anet, E. F. L. J. Carbohydr. Res. (1968) 8:164; Micheel et al. Justus Liebigs Ann. Chem. (1933) 502:85; Ward et al. Can. J. Chem. (1994) 72:1429; McAuliffe et al. Synlett. (1998) 307; Contour et al. Carbohydr. Res. (1990) 201:150.
Additionally, the synthesis of septanose glycals has been described via tungsten-catalyzed cycloisomerization of terminal alkynyl alcohols. Alcázar et al. Org. Lett. (2004) 6:3877; Koo et al. Org. Lett. (2007) 9:1737. Recently, Peczuh et al. provided considerable insight into the preparation and functionalization of septanose carbohydrates. Peczuh et al. Carbohydr. Res. (2004) 339:1163; Fyvie et al. Carbohydr. Res. (2004) 339:2363; DeMatteo et al. J. Org. Chem. (2005) 70:24; Castro et al. J. Org. Chem. (2005) 70:3312; Castro et al. Org. Lett. (2005) 7:4709.